Ethylene glycol is an important chemical raw material and strategic material in China, which is used for producing polyester, which may be further used for producing terylene, PET bottles, and thin films, explosives, and glyoxal, and may be used as an antifreeze agent, a plasticizer, a hydraulic fluid, a solvent, etc. In 2009, the amount of imported ethylene glycol of China exceeded 5.80 million tons. It is predicted that the demand for ethylene glycol in China will be up to 11.20 million tons by 2015, while the throughput is about 5.00 million tons, and the gap of supply and demand is still up to 6.20 million tons. Therefore, the development and the application of new techniques for producing ethylene glycol in China have a good market prospect. In the world, ethylene from petroleum cracking is mainly used to obtain ethylene oxide by oxidation, and ethylene glycol is obtained by the hydration of ethylene oxide. In view of current situations such as the energy resource structure of “rich coal, insufficient oil, and little gas” in China, the price of crude oil running at a high level for a long term, etc., new coal chemical techniques for preparing ethylene glycol from coal can both ensure the national energy security and fully utilize coal resource in China, and are the most realistic selection for the coal chemical industry in the future.
At present, a relatively mature domestic technique is “a packaged processing technique for synthesizing oxalate by gas phase catalysis of CO and synthesizing ethylene glycol by catalytic hydrogenation of oxalate” developed by Fujian Institute of Research on the Structure, Chinese Academy of Sciences. In early December of 2009, the first set of industrialized apparatus attracting a large number of attentions in the industry in the world—the first phase construction of “project for preparing ethylene glycol from coal” by Tongliao Jinmei Chemical Corporation, Inner Mongolian, which was a project for preparing ethylene glycol from coal with an annual production of 200 thousand tons, opened up the whole process flow, and produced a qualified product of ethylene glycol. However, the economy, the environmental protection property, the energy saving property, and the further engineering scaling-up of this process flow will be restricted by the large number of processing units, the high requirement for the purity of industrial gas, the need for the use of precious metal catalyst in the process of oxidative coupling, the need for the use of nitrogen oxides which potentially pollute the environment, and the like.
Polyoxymethylene dimethyl ether (or referred to as polyoxymethylene methylal) has a molecular formula of CH3O(CH2O)nCH3 wherein n≧2, and is typically simply referred to as DMMn (or PODEn). In the process of the preparation of polyoxymethylene dimethyl ether, the distribution of products generated is unconscionable. Methylal and DMM2 are relatively high, while the selectivity of DMM3-4, which may be used as a diesel additive, is relatively low. Therefore, byproducts in the preparation process thereof are often required to be subjected to repeated separation and further reaction, and this consumes a large amount of energy and has a bad economy. Therefore, if methylal and DMM2 as byproducts can be directly processed into a product having a higher economic value, the economy of this process will be increased.
In recent years, the research team of Professor Alexis T. Bell at UC, Berkeley, U.S., proposed a new scheme, wherein methyl methoxyacetate is prepared by using a gas phase carbonylation method of methylal and ethylene glycol is then obtained by hydrogenation hydrolysis, and wherein the most important step is the reaction of gas phase carbonylation. However, the catalyst has a short service life, the raw material gas has a low concentration of methylal, neither the conversion rate of methylal nor the selectivity of methyl methoxyacetate is desirable, and there is a considerably long distance from industrialization. [Angew. Chem. Int. Ed., 2009, 48, 4813-4815; J. Catal., 2010, 270, 185-195; J. Catal., 2010, 274, 150-162; WO 2010/048300 A1].